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Toxins That Affect the Mitochondria

How might mitochondria be affected by toxic chemicals? Mitochondrial toxins fall into three categories. They can: Toxic Barrel Image

  1. Inhibit electron transport. Interfere with the transport of electrons through the chain of proteins in the electron transport system (examples: fungicides, some herbicides)
  2. Uncouple phosphate bonding. Prevent the creation of high energy phosphate bonds - without affecting electron transport [ex: cyanide]
  3. Have mixed action. Act as in type 1 at high doses and act as in type 2 at low doses (example: herbicides)

Electron Transport Inhibitors
Environmental toxins such as herbicides, insecticides, and fungicides can prevent the passing of electrons by binding to one or more of the proteins that carry electrons. Examples:

  • Insecticide: (rotenone) 
  • Fungicides: (carfboxin, oxycarboxin, and fenfuran) 
  • Herbicides: (chlorproham, propanil, dinoseb, and ioxynil.) 
Cyanide is a well-known poison that prevents the addition of high energy phosphate groups to make the energy storage compound, ATP.  Other well-known compounds that act this way include the pesticides pentachlorophenl (PCP) and 2,4-dinitrophenol (DNP).

Mixed Action Toxins
Certain herbicides inhibit electron transport at high concentration and promote uncoupling at low concentrations. Some insecticides, such as DDT and cyclodiene, are also in this group.

Something to Think About

Part of the way that these toxins act comes from their ability to penetrate and stick in membranes.  Recall that when any compound gets incorporated in a membrane, as in our previous alcohol example, it can disturb the position of the other compounds that are normally found there. In the membranes that make up the folds inside of mitochondria, such disturbance interferes with the  passing of electrons that is needed to couple energy to ATP synthesis.

Here is a question to think about: Could herbicides and insecticides affect processes in other membranes, such as those in the nuclear membrane or membranes where proteins are made (endoplasmic reticulum), or even the cell membranes of excitable cells such as nerve cells?


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